Where does “Albain” come from?

Albain (Old Irish) comes from Old Irish Albu, from Proto-Celtic albiyū, from Proto-Indo-European h₂élbʰos — white.

Ancestry of “Albain”, step by step

Step	Language	Word	Meaning
1	Old Irish	Albu	Britain, Scotland
2	Proto-Celtic	albiyū	luminous world, upper world, world; high...
3	Proto-Indo-European	h₂élbʰos	white

Albain — Etymology, Origin & Word History | Etymology Explorer